This invention was made under contract with or supported by the Electric Power Research Institute.
1. Field of the Invention
This invention relates to electric power conversion and particularly to a utility power system wherein a direct-current power source is coupled to an alternating current utility power network.
To meet increasing power demands placed upon electric utilities, it is necessary to couple electric power from a variety of sources into a compatible network for transmission and distribution. Many of the power sources, particularly those derived from emerging technologies such as fuel cells, batteries, magnetohydrodynamics and superconducting magnetic energy storage, provide or store electric power in the form of direct-current. Electric power thus provided must be interfaced with existing energy transmission and distribution networks with a minimum of power loss.
In addition, potential economic advantages exist for dispersed energy storage and generation techniques. For example, dispersed energy generation permits location of generation nearer the load centers, possible deferral of other expenditures for transmission and distribution equipment, and can increase the reliability of the bulk power supply system. Thus, it is considered desirable to provide self-contained energy conversion and storage power conversion units, in order to permit increased system flexibility.
In the development of energy conversion equipment great stress is laid on component reliability. Thus, DC/AC power conversion equipment must be highly reliable. Partly for this purpose attention is concentrated on the development of high power solid-state devices, such as thyristor or p-n-p-n type externally switchable rectifier circuitry, and the development of systems utilizing solid state devices. However, until relatively recently, solid-state devices with the potential power handling capability to perform power system related tasks have not been readily available.
2. Description of the Prior Art
Power conversion units based on voltage-fed forced commutation as the turn-off mechanism of a thyristor, or silicon controlled rectifier (SCR), are known for coupling DC and AC power systems. Voltage-fed force commutated converters of conventional design require auxiliary control and firing circuitry. In practice, over the broad power factor and voltage ranges contemplated, it is relatively difficult to achieve economical reliable, and efficient system operation with conventional voltage-fed converter configurations. Voltage-fed power converters must be capable of acceptable operating efficiency over a range of voltage levels. For example, battery-fed converters must operate over the useful voltage range of the batteries, which may be a ratio of peak-to-minimum voltage of 1.5 to 1.0.
Current-fed naturally-commutated energy conversion units are known for high voltage direct-current (HVDC) transmission applications.
So far as is known a naturally-commutated voltage-fed power converter has not been proposed.